Could recurrent left groin odor after clindamycin treatment be due to erythrasma or apocrine bromhidrosis with secondary bacterial overgrowth?

Diagnostic Approach to Recurrent Left Groin Odor

Your asymmetric presentation with dramatic day-1 clindamycin response most likely represents apocrine bromhidrosis with secondary bacterial overgrowth rather than erythrasma, but you cannot definitively rule out localized erythrasma without Wood's lamp examination showing coral-red fluorescence. 1

Why This Probably Isn't Erythrasma

The evidence against erythrasma in your case includes several key features:

• Rapid response pattern: Your near-complete odor resolution on day 1 of topical clindamycin argues against erythrasma, because Corynebacterium minutissimum colonizes deeper in the stratum corneum and typically requires 3-5 days to show improvement even with appropriate therapy 1, 2

• Strictly asymmetric severity: While erythrasma can present with asymmetric intensity based on local moisture differences, the fact that your right side cleared completely with one course and stayed clear suggests this isn't a bilateral colonization pattern typical of Corynebacterium 1

• Absence of visible changes: Erythrasma usually produces at least subtle brown or pink patches with fine scaling, though purely odor-based presentations can occur in early disease 1

Why Bromhidrosis Is More Likely

Your presentation fits apocrine bromhidrosis with bacterial overgrowth:

• Anatomic distribution: The left groin where your anatomy creates more moisture/occlusion is exactly where apocrine glands concentrate and where anaerobic bacteria metabolize apocrine secretions into volatile fatty acids that cause pungent odor 3

• Environmental correlation: Your bed-rotting habit with duvet creates the perfect anaerobic, high-humidity environment for bacterial metabolism, and the right side staying clear after eliminating those factors on that side proves local conditions drive this 3

• Rapid antibiotic response: Surface bacterial overgrowth (Staphylococcus, mixed anaerobes, or Corynebacterium species acting as commensals rather than tissue-invasive pathogens) responds within 24-48 hours to topical clindamycin 2

The Biofilm Question: Not Your Primary Problem

You do not need to aggressively target follicular biofilm because your day-1 response proves this is surface colonization, not deep follicular infection. 4

Here's why biofilm is unlikely:

• Response kinetics: Biofilm-protected bacteria show delayed or incomplete antibiotic response because the extracellular matrix shields organisms from antimicrobial penetration—your near-immediate clearing contradicts this 4

• Hair density irrelevant: Even vellus (fine) hairs harbor bacteria in follicular canals, but biofilm formation requires chronic infection (weeks to months) with tissue invasion, not the acute relapsing pattern you describe 4

• Right side clearance: If biofilm reservoirs were driving recurrence, both sides would relapse symmetrically since follicular anatomy is bilateral 4

Your recurrence at one month reflects environmental recolonization (moisture/occlusion allowing surface bacteria to regrow) rather than persistent deep reservoirs 3

Definitive Diagnostic Strategy

Get Wood's lamp examination before any further clindamycin courses if you relapse within 2-4 weeks despite perfect environmental control. 3, 1

Wood's Lamp Interpretation and Management

Coral-red fluorescence = Erythrasma confirmed 1

• Oral erythromycin 250 mg four times daily for 14 days is curative (not just suppressive like topical clindamycin) 3, 2
• Alternative: Oral azithromycin 500 mg daily for 3 days if erythromycin intolerance 3
• After oral therapy, continue benzoyl peroxide 2.5% wash 1×/week indefinitely as prophylaxis 3
• Topical clindamycin fails for erythrasma because it doesn't penetrate the full thickness of colonized stratum corneum where Corynebacterium lives 1, 2

No fluorescence = Bromhidrosis with bacterial overgrowth 3, 1

• Obtain bacterial culture/swab of the perimeter to identify specific organisms 3
• If culture grows methicillin-sensitive Staphylococcus aureus: oral clindamycin 150 mg daily for 3 months prevents recurrent staphylococcal skin infections with 82% success rate and durable response in 67% of patients after stopping 5, 4
• If culture grows anaerobes or mixed flora: switch to topical metronidazole 0.75% gel applied to perimeter nightly for 7 days, then 2×/week maintenance—metronidazole has superior anaerobic coverage with minimal systemic absorption (4% bioavailability) 4, 3

Your Current Management Plan

Complete your current 5-day clindamycin course as planned, then implement strict environmental control before considering any further antimicrobial therapy. 3

Post-Clindamycin Protocol (Starting Day 6)

Maintenance antimicrobial strategy:

• Benzoyl peroxide 2.5% wash to perimeter 2×/week (Monday and Thursday)—apply for 2-3 minutes, rinse thoroughly 3
• Vinegar swipe (dilute white vinegar on cotton pad) 1×/week on separate day from BP to acidify skin surface and inhibit bacterial growth 3
• Do NOT use clindamycin for maintenance—topical clindamycin provides no benefit over BP for prevention and risks resistance development 3

Non-negotiable environmental modifications:

• Eliminate duvet entirely—switch to single cotton sheet or lightweight blanket for air circulation 3
• Post-void ritual after every urination: 10-second plain water rinse, pat dry with dedicated towel, 10-15 seconds cool blow-dryer on low speed to left perimeter 3
• Sleep positioning: right side or supine with legs slightly apart to prevent left-sided compression 3
• Pouch-style moisture-wicking briefs (not cotton), change immediately if sweating or dribble, hot-wash ≥60°C without fabric softener 3
• Hot-wash ALL underwear, sheets, and towels NOW to eliminate fomite recolonization 4

Relapse Definition and Escalation Triggers

Define relapse objectively: Return of pungent/fishy odor to ≥60-70% of original intensity, persisting ≥3 consecutive days despite washing and dryness measures 3

If Relapse Occurs

First response (before repeating clindamycin):

• Intensify dryness: add midday blow-dry session, eliminate all bed-sitting, check for new moisture sources 3
• Increase BP to 3×/week for 7 days 3

If odor persists after 7 days of intensified measures:

• Get Wood's lamp examination before repeating clindamycin 3, 1
• If Wood's lamp unavailable and relapse occurs within 2-4 weeks despite perfect environmental control, empirically treat as erythrasma with oral erythromycin or azithromycin 3

If you require ≥2 clindamycin bursts within 6-8 weeks:

• Wood's lamp examination is mandatory 3
• Bacterial culture/swab to identify specific organism and guide targeted therapy 3

Why Your Right Side Staying Clear Matters

The unilateral persistence after bilateral initial involvement proves this is environmentally driven, not a systemic colonization issue. 3

This pattern confirms:

• Your anatomy (where body part rests) plus sleeping position (left side down under duvet) creates localized moisture/occlusion on the left 3
• The causative organism (whether Corynebacterium, Staphylococcus, or anaerobes) requires specific environmental conditions to proliferate 3, 1
• Fixing the environmental factors will likely achieve long-term clearance without chronic antimicrobial therapy 3

Common Pitfalls to Avoid

Do not repeat clindamycin bursts without diagnostic confirmation if you relapse—this creates antibiotic resistance without addressing the underlying cause 3

Do not use topical clindamycin for maintenance—it provides no prophylactic benefit and clears from tissue within 3-8 days 4, 3

Do not skip the environmental modifications—your bed-rotting habit is the single biggest modifiable risk factor, and no amount of antibiotics will work if moisture/occlusion persists 3

Do not assume this is erythrasma without Wood's lamp confirmation—the treatment differs fundamentally (oral vs topical antibiotics), and misdiagnosis leads to treatment failure 3, 1, 2